Dawn of the Dead ('04), Land of the Dead ('05), The Crazies ('10), I am Legend, 28 days/weeks later, World War Z, Planet Terror, Quarantine...
Didn't include the comedy ones.
Dead snow is fantastic but I wouldn't call it serious. I really like 28 Days Later.
Actually, what the one that takes place in Africa? ThaThe Deat's one of the best.
The Dead.
There's another good one during civil war time called Exit Humanity